In data processing systems, data is stored in a variety of devices, such as, for example, main memory, magnetic disk, magnetic tape, optical disk, etc. Whatever the storage medium, it is essential that the data be correctly written on the medium and correctly retrieved. Although the degree of reliability provided by storage devices is high, there will be failures influencing the accuracy of information stored or read from time to time. As a consequence, error detection and correction techniques have been developed and have been in use for many years. The theory of redundant storage techniques and devices practicing those techniques are based upon error correcting codes, such as described in ERROR CORRECTING CODES, Second Edition, W. W. Peterson and E. J. Weldon, Jr. the MIT PRESS 1972, and Richard E. Blahut THEORY AND PRACTICE OF ERROR CONTROL CODES, Addison Wesley, Redding, Mass. 1983.
In the various error correcting codes, the ability to detect and correct errors is increased when the code module receives a pointer to particular data that is in error, or suspected to be in error. Essentially, the power of the error detection and correction code circuitry is doubled when a pointer to an error is provided. The invention to be described herein relates to an improved technique for the generation and processing of such pointers. The invention is useful regardless of the technology in which error correcting code techniques are utilized and it is beneficial to all codes. For example, the invention is useful in correcting errors on magnetic disk or tape, optical disk or tape, or any other type of transmitting device employing error correction.